Project Summary (Public Abstract) The violent conflict of war always results in amputees. After World War II, a team of well-known clinician scientists led by H. D. Eberhart examined the biomechanics of human gait and reported to the National Research Council Committee on Artificial Limbs, advisory to the Veterans Affairs and the Office of the Surgeon General of the United States Army, that transverse plane motions and their frictional effects are a major source of discomfort and the chief cause of dissolution of the skin in lower limb amputees. This was quite remarkable given the state-of-the-art of prosthetic limbs in 1947. Identifying a problem is one thing, solving it is another. Thirty years went by before Lamoureux and Radcliffe reported in 1977 that a greater degree of freedom in the transverse plane of the prosthesis might improve the changing of direction of ambulatory amputees. As our own research suggests that turning maneuvers comprise about 30% of daily steps, it is not too surprising that evidence in the literature reports the benefits of commercially-available torsion adapters to include improved walking performance, reduced metabolic costs, the potential to reduce residual limb soft tissue injuries, and improved balance and stability. While these devices are available for prescription, a glaring problem remains. None of the commercially-available transverse plane torsion adapters can be adjusted by the user. When patients are fit with these devices, the prosthetist sets the stiffness and that is it. The selected stiffness is expected to be adequate for all of an amputee's activities. To address this deficiency, we developed a novel prosthesis whose transverse plane stiffness can be adjusted by the user. The specific aims of the proposed research are to determine: (1) the preferred transverse plane stiffness and (2) the transverse plane stiffness that minimizes the transverse plane moment applied to the residual limb of Veteran lower limb amputees during different ambulatory activities at different speeds. We believe this research will significantly improve the function and quality of life of Veteran lower limb amputees. Developing new technology that allows the prosthetic limbs of Veteran amputees perform like a natural limb is where the VA should be: at the forefront of prosthetic technology and prescription practice.